GCN Circular 21486

J. Y. Liao, C. K. Li, M. Y. Ge, Y. Huang, S. L. Xiong, Y. Liu,
C. Z. Liu, X. F. Li, Z. W. Li, Z. Chang, X. F. Lu, J. L. Zhao,
A. M. Zhang, Y. F. Zhang, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU),
T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, H. Y. Wang, M. Wu, Y. P. Xu,
S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team:

Insight-HXMT was taking data normally around the LIGO trigger time
(T0=2017-08-14 10:30:43 UTC). At T0, more than 95% of the LHV
localization region was covered by the Insight-HXMT without occultation
by the Earth. However, the general direction of the LHV localization is
almost perpendicular to HXMT detectors and thus the sensitivity of HXMT
is almost the worst.

Within T0 +/- 1000 s, no significant excess (SNR > 5) is found
in a search of the Insight-HXMT raw light curves with time bins of
20 ms, 50 ms, 0.2 s and 1 s, respectively. Within T0 +/- 100 s for
SNR>3, there is one 3.3 sigma excess only for the time bin of 0.2 s
at 10 s before T0, completely consistent with background fluctuations.

With the three typical GRB Band spectral models, three integration time
(1 s, 10 s, and 100 s) and the LHV localization region, the 3-sigma
upper-limit fluence (0.2 - 5 MeV, incident energy) are reported below:

Band model 1 (alpha=-1.9, beta=-3.7, Ep=70 keV):
1s: 2.2e-07 to 3.3e-07 erg cm^-2
10s: 7.5e-07 to 1.2e-06 erg cm^-2
100s: 2.6e-06 to 4.1e-06 erg cm^-2

Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV):
1s: 3.4e-07 to 5.0e-07 erg cm^-2
10s: 1.2e-06 to 1.7e-06 erg cm^-2
100s: 4.0e-06 to 5.9e-06 erg cm^-2

Band model 3 (alpha=0.0, beta=-1.5, Ep=1000 keV):
1s: 7.5e-07 to 9.9e-07 erg cm^-2
10s: 2.4e-06 to 3.2e-06 erg cm^-2
100s: 8.6e-06 to 1.0e-05 erg cm^-2

All measurements above are made with the CsI detectors operating in the
regular mode with the energy range of about 80-800 keV (record energy).
Only gamma-rays with energy greater than about 200 keV can penetrate
the spacecraft and leave signals in the CsI detectors installed inside
of the telescope.

The analysis results presented above are preliminary;
refined results will be reported later.

Insight-HXMT is the first Chinese space X-ray telescope, which was funded
jointly by the China National Space Administration (CNSA) and the Chinese
Academy of Sciences (CAS). More information about it could be found at:
http://www.hxmt.org/index.php/enhome .